Juxtaposition of India and Madagascar: A perspective

Proterozoic terrains in South India and Madagascar provide important clues in understanding the Gondwanaland tectonics, especially the assembly of thi s mega-continent during the Pan-African period. The Archaean terrains in bo th Madagascar and India are characterized by N-S trending greenstone belts occurring within gneissose granitic rocks in the northern part. Extensive d evelopment of K-rich granitic rocks of ca. 2.5 Ga is also characteristic in both areas. Such a broad age zonation of younger Dharwar (ca 2.6-3.0 Ga) i n the north and the older Sargur (ca 3.0-3.4 Ga) in the south as in South I ndia remains to be identified in future studies from Madagascar. The occurr ence of greenschist facies rocks in the northeastern part and higher grade rocks in most of other parts in the north-central terrain of Madagascar is comparable with the general tendency of increasing metamorphic grade from n orthwestern to southern areas ranging from greenschist to granulite facies in South India. The Proterozoic crystalline rocks in both continents show p ronounced lithological similarity with the wide occurrence of graphite-bear ing khondalite in association with charnockitic rocks. While the Archaean-P roterozoic boundary is well defined in southern India by the Palghat-Cauver y or the KKPT shear zones as recently identified, this boundary is ill-defi ned in Madagascar due to extensive Pan-African overprinting, as well as the development of the Proterozoic cover sequence, the Itremo Group. There is also a possible general correlation between the Mesoproterozoic cover seque nces in Madagascar and India, such as between the Itremo Group of west-cent ral Madagascar and the Kaladgi and Cuddapah sequences of South India. The P an-African granulite facies metamorphism of ca. 0.5 Ga extensively develope d in both India and Madagascar is generally comparable in intensity and ext ent. P-T conditions and P-T-t paths also appear comparable, with the genera l range of cn. 700-1000 degrees C and 6-9 kb, and near-isothermal decompres sional paths. A-type granite plutons and alkaline rocks including anorthosi tes and mafic plutonic rocks of ca. 500-800 Ma develop in both terrains, pr ovide strong basis for the correlation of both terrains, and define a Pan-A frican igneous province within East Gondwanaland. Major shear zones in both continents are expected to play a critical role in the correlation, albeit are still poorly constrained. Detailed elucidation of the tectonic history of the shear zones, and the timing of various events along the shear zones would provide important constraints on the correlation of the two continen tal fragments.